Induction of translatable mRNA for dopa decarboxylase in Drosophila: an early response to ecdysterone.

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Abstract
Ecdysteroid titer and dopa decarboxylase (aromatic-L-amino-acid carboxy-lyase, EC 4.1.1.28) activity were determined throughout the life cycle of D. melanogaster. Five peaks in the amount of hormone were observed, which preceeded 5 dopa decarboxylase peaks by times ranging from 5-58 h. Late in the 3rd instar the hormone and enzyme maxima are nearly coincident. The increase in enzyme activity observed at this time is paralleled by an increase in translatable dopa decarboxylase mRNA. To obtain evidence that ecdysterone induces the appearance of this mRNA the temperature-sensitive ecd1 mutant was used. Garen et al. (1977) showed that when 3rd instar mutant larvae are kept at 29.degree. C, the ecdysteroid titer remains low. In such larvae the normal increase in dopa decarboxylase activity fails to appear, and no translatable dopa decarboxylase mRNA can be detected. Exogenous feeding of ecdysterone to these larvae results in a rapid synthesis of dopa decarboxylase in the epidermal cells. A parallel increase in translatable dopa decarboxylase mRNA occurs, which may be a primary response of these target cells to ecdysterone.